1. Field of the Invention
This invention relates to means for securing members to structures, and particularly to a new and improved means and a method for securing a blade retainer to a rotor disc.
2. Description of the Prior Art
The rotor blades of a turbomachine are commonly attached to the rotor disc of the machine by insertion of a dovetail of each rotor blade into a correspondingly shaped axial slot in the disc. This arrangement prevents radial and tangential movement of each rotor blade relative to the rotor disc. In order to prevent axial movement of the rotor blades, one or a plurality of blade retainers are disposed adjacent the axial slots in the rotor disc. The blade retainer must be secured to the rotor disc strongly enough to resist the forces exerted on it by the dovetails of the rotor blades, and yet it must be easily removable in order to replace the rotor blades.
Many currently-used blade retainers are secured to rotor discs by bolting. Although the bolts provide a strong connection between the blade retainer and the disc, their use also presents some problems. For example, securing and replacing the blade retainer requires corresponding installation and removal of the bolts and their nuts, an operation which can be time consuming. The bolts must be carefully torqued in order to avoid overstress at the connection, which can also be time consuming. The holes located in the blade retainer and disc and through which the bolts extend can cause fatigue cracks in the retainer and disc. Such cracks can shorten the useful life of those parts resulting in higher costs to the user. Bolt heads and nuts protruding from the disc increase the temperature of the surrounding air and increase the disturbance of the airflow, or windage, across the disc resulting in decreased engine performance.
Recently, boltless blade retainers have been introduced in order to alleviate many of the above-mentioned problems. An example of such a boltless blade retainer is shown in U.S. Pat. No. 3,768,924, issued to R. J. Corsmeier et al, assigned to the same assignee as the present invention, and the disclosure of which is incorporated herein by reference.
Although such boltless blade retainers have successfully eliminated many of the aforementioned problems, some difficulties have remained unsolved. For example, in order to secure the blade retainer to the disc, many boltless blade retainers utilize a plurality of tabs on the radially inner portion of the blade retainer which interlock into a plurality of slots on the disc. Although effective for securing the blade retainer to the disc, the fabrication of such a tab/slot arrangement requires the step of machining each of the tabs and slots, which can be time consuming and increase costs. The slots in the disc and tabs protruding from the blade retainer can increase the change of development of fatigue cracks in both the disc and blade retainer, which can shorten useful life. The tabs protruding from the blade retainer cause a disturbance of airflow, or windage, across the disc, which can reduce engine performance.
Other kinds of boltless blade retainers utilize means such as clips or shear wires to secure the blade retainer to the disc. Although these means are also effective for securing the blade retainer to the disc, they present associated problems similar to those of the tab/slot arrangement.
In view of the above-mentioned problems, it is therefore an object of the present invention to provide a structurally simple and therefore inexpensively fabricated means for securing a blade retainer to a disc.
Another object of the present invention is to increase the useful life of the blade retainer by eliminating holes or slots in it which thereby decreases the opportunity for fatigue cracks to develop.
Another object of the present invention is to reduce windage, or disturbance of the airflow, across the disc by decreasing the protrusions from the blade retainer and the disc.
Yet another object of the present invention is to provide a method for quickly and simply securing a blade retainer to a disc.